Titan Mode is a Dependent Perk offered after taking triple jump .
When you have it, jumping on enemies deals damage of 100x Loadout Attack for regular enemies (including minions spawned by bosses) but only 5x for bosses.
When in Titan Mode (i.e. actually jumping on an enemy, not just having the perk) you are supposedly immune to damage from below but there have been cases (say, last boss in World 9) where the immunity has failed
It’s fun to do Titan mode on a boss just under a barrier - then your rebound is curtailed so you hit much more rapidly